3.2.2. Thermal Conductivity

Figure 7 shows the thermal conductivity of (Ti50Al50)N, (Al66Ti34)N, and (Al70Cr30)N coatings [67]. The thermal conductivity is temperature-dependent and it is interesting to note that the thermal conductivity of (Al70Cr30)N drops at about 200 ◦C and, in the temperature range of 250–450 ◦C, is significantly lower than that of (Al66Ti34)N. The thermal properties of Cr25Al20.5Si4.5N50 coatings were measured using pulsed photothermal radiometry. A very low thermal conductivity of ca. 2.75 W/mK at room temperature and 3.5 W/mK at 400 ◦C was found [68]. PVD coatings exhibit a certain anisotropy of thermal conductivity perpendicular and parallel to the direction of growth. This effect is particularly pronounced for multilayer coatings. When engineering the thermal properties of a coated part, not only the intrinsic thermal conductivity of the coatings, but also the concentration and dimension of different growth defects, e.g., holes and droplets, must be taken into account [69].

**Figure 7.** The temperature dependence of thermal conductivity for arc-deposited (Ti50Al50)N, (Al66Ti34)N and (Al70Cr30)N coatings, measured using the picosecond thermal reflection method, redrawn after [67], original © Elsevier.
